For applications like portable electronics and automotive, e.g. for use in (hybrid) electric vehicles (EVs, PHEVs), battery systems are desired with optimal energy densities to provide minimal system weight and volume. To enable high energy densities, lithium metal based batteries (i.e. with lithium metal as anode) are appealing since the energy density of the metal can reach high levels of about 3800 mAh/g. U.S. Pat. No. 6,168,884 discloses a planar design of a lithium metal anode that is formed in-situ during initial charge by plating lithium on an anode current collector, which does not form inter-metallic compounds with lithium. The anode current collector is sandwiched between a solid state electrolyte and an overlying layer.
It is also known to have a rechargeable Li-ion solid-state battery with a current collector of non-planar design. Thin-film battery structures of known type are disclosed e.g. in WO2010032159, the contents of which are included by reference, wherein for example all-solid state compositions are deposited on 3D micro-patterned structures. In this respect, where early battery structures utilize liquid electrolytes, all-solid state compositions utilize electrolytes of a solid state type, which are inherently safer in use. In these structures a large variety of materials are and have been used for the respective electrodes for example as disclosed in US 20110117417.
DE102011121681 discloses a pillar geometry for a liquid electrolyte, wherein dendrites are prevented from forming on the pillar tops by isolating these. The pillars are extending in an electrolyte fluid or gel and distanced from a cathode sheet.
In discharging battery mode, the anode is the “negative electrode” to which the positive current flows, from the cathode, being the “positive electrode”. During charge these functions are reversed. Irrespective charging mode, the electrochemical relationship may be characterized by charge exchange between a negative electrode material and a positive electrode material, the negative electrode material having a workfunction or redox potential that is lower than the workfunction or redox potential of the positive electrode material.
For example, known negative electrode (anode) materials are Li4Ti5O12 (LTO); LiC6 (Graphite); Li4.4 Si (Silicon) and Li4.4Ge (Germanium) known positive electrode (cathode) materials are LiCOO2 (LCO), LiCoPP4, (doped) LiMn2O4 (LMO), LiMnPO4, LiFePO4 (LFP), LiFePO4F(LFPF), LiCO1/3Ni1/3Mn1/3O2 (LCNMO), Sulphur or Sulphur based compounds like LixS.
Known (solid state) electrolytes might include Garnets such as Li7La3Zr2O12 (LLZO), Perovskites such as La0.57Li0.33TiO3 (LLTO), lithium iodide (LiI), lithium phosphate (Li3PO4) and lithium phosphorus oxynitride (LiPON). In addition, lithium salts, such as LiPF6, LiBF4 or LiClO4 in an organic solvent, such as ethylene carbonate, dimethyl carbonate, diethyl carbonate, propylene carbonate are known to have a typical conductivity of about 10 mS/cm at RT. The electrolyte decomposes on initial charging and forms a solid layer called the solid electrolyte interphase (SEI).
Solid polymer separators like polyethylene oxide (PEO) may also be included, such polymers having transport capacity often due to having a lithium salt disposed therein as known in the state of the art. Work has also been performed with lithium and halide materials, particularly, in some examples, a lithium aluminum tetrahalide such as lithium aluminum tetrafluoride (LiAlF4).
Once such structures are made on a bendable metal foil, they can be manufactured in large-scale processes, e.g. a roll-to-roll process where the following can be done: 1) Coiling, winding or stacking it to increase the energy or power density per unit volume. 2) Integrating it on flexible devices like flexible displays, signage etc.
Although high-aspect ratio structures can be made in nanometer scale the height or depth of these high-aspect ratio structures need to be in the microns range for delivering enough charge capacity for the battery. The reason why these structures are preferred is due to the easy accessibility of their entire surface. In the prior art many methods to produce these are non-economical (e.g. involving silicon microfabrication and long-time electrodeposition). Moreover, to do any of these, the design of the stack is in need for optimization because otherwise while winding or flexing, the pillar structure could be damaged inhibiting proper electrochemical action of the device. Furthermore, it has come to the attention that existing solid state (e.g.) Li-based intercalation electrolytes induce stress in the high-aspect ratio structures that may limit lifetime and reduce the number of cycle periods. A challenge exists to minimize the relative amount of electrochemically inactive electronic current collectors without compromising on the rate performance. It is aimed to provide a method and structure for a 3D thin film battery design, having an all-solid state structure to provide a design with both inherent safety and high energy densities.